64 Spalding : M 



During the observations, it became evident that while the 

 plant as a whole responded in the way described to variations in 

 its water-supply, different parts of the stem were affected in differ- 

 ent degrees, and to such an extent that one furrow might even be 

 contracting while another on the same plant was expanding. 

 These facts are most evident from the records of plants that were 



not watered. 



The lowest points at which measurements were made always 

 showed a slow rate of change, and for a few inches below the apex 

 the width of the furrows was stationary. Although observations 

 were not sufficient to demonstrate any law as to comparative rate 

 of change in different parts of the stem, a comparison of the curves 



figiir 



show that the 



variation near the base is less than higher up on the trunk. 



This difference in the rate of change at various heights of the 

 stem is no doubt mainly due to the different proportion of mechan- 

 ical and water-storing tissue as shown \n figures 5, 6 and 7 repre- 

 senting sections taken at 8 feet, 5 feet, and i 5 inches from the base 



of a plant 9, feet high, but the different consistency of the cell-con- 

 tents ip the upper and lower parts of the stem may also be a factor. 

 The fact that no two furrows on the same stem vary exactly 

 alike, even when measured at the same height, may also be under- 

 stood by reference to the same figures. The contour of the sections 

 shows that, beginning at the top, where the furrows are nearly 

 equal all around the stem, their width and depth on opposite sides 

 differ more as we pass to the lower portions. The deeper and 

 narrower furrows are on the south ; and the wider, shallower ones 

 on the north side of the stem ; and as we pass down to the suber- 

 ized tissue near the base of the larger individuals the furrows all 

 become obliterated and the ribs are finally marked only by rows 

 of spines. 



A 



(/. 



is greater on the south than on the north side, and that while the 

 southern furrows may begin to expand earlier, the northern ones 

 expand longer. This difference in action of the two sides corre- 

 sponds with the configuration of the mature stem, and suggests an 

 mteresting inquiry regarding the combined influence of temperature 



